PVdF-based coatings are known to be very useful as protective coatings for a variety of substrates. These coatings are thermally stable and are resistant to weathering and chemical degradation.
The general technique used for preparing PVdF-based coatings entails; preparing a dispersion of PVdF in a suitable solvent, applying this dispersion by conventional means onto the required substrate, then subjecting this substrate to heat treatment. The solvent used in the dispersion is generally known in the art as "latent solvent", and is described as an organic solvent which has no significant action on PVdF at room temperature but which at an elevated temperature exerts a sufficient solvent action.
Although the known systems may give good results, environmental protection laws throughout the world, but mainly in the U.S.A. and Europe, are making it increasingly difficult to handle solvent-based coating systems. Further, the recovery of the solvent is a costly procedure. Accordingly, there is a significant need for solventless PVdF-based coatings.
It is also known in the art to obtain pigmented PVdF-based coatings from a mixture of powdered pigment and PVdF. However, such a mixture is hardly homogeneous. Further, the pigment is not perfectly wetted by the resin, and the coatings obtained have no long term stability (believed to be due to the presence of voids around the pigment particles). Also, the mechanical properties of such coatings are rather bad. Accordingly, there is a significant need in the art for an improved solventless process for obtaining pigmented PVdF-based coatings.